"Team was playing defensively" doesn't really fly as an explanation for Ovechkin's "decline". Majority of the damage he did was either off the rush (and not even odd-man rushes; he generated chances consistently on 2 on 2s or 2 on 3s) or on the powerplay--not on, say, a balls to the wall forechecking system or an aggressive cycle where the D pinch like crazy. If Boudreau started having them trap in the neutral zone, that shouldn't have cut down on powerplays all that much and shouldn't have cut down on rushes almost at all.

Moreover, when Hunter really dialed back on players leaving the zone early and tried to generate offense off the cycle, that's something that would make sense in shredding Ovechkin's goal totals bad (its a strategy that's completely unsuited to his game), but, if I'm not mistaken, they actually went up relative to what they were in Boudreau's "trap."

Coaches knew what he liked to do by his second season at the latest. He still executed, so that explanation doesn't work either.

Some of you are looking for complicated answers to a simple situation. The obvious fact that anyone with eyes can see is that his burstability (and the frequency with which he showed it) is not what it once was. Whether he lost explosiveness due to conditioning, desire or age is anybody's guess.

Edit: one more thing. Backstrom being out shouldn't enter into it. The player OV was didn't need a playmaker and Backstrom generates from within the offensive zone, not in making his team get there quickly. But Green being out (and a shell of himself when he did play) would make sense as a contributing (but not primary) factor, since Green generates rushes.